Evaluation of whole genome amplification protocols for array and oligonucleotide CGH

Systematic comparison of two whole-genome amplification methods for targeted next-generation sequencing using frozen and FFPE normal and cancer tissues

Sequencing key cancer-driver genes using formalin-fixed, paraffin-embedded (FFPE) cancer tissues is becoming the standard for identifying the best treatment regimen. However, about 25% of all samples are rejected for genetic analyses for reasons that include too little tissue to extract enough high quality DNA. One way to overcome this is to do whole-genome amplification (WGA) in clinical samples, but only limited studies have tested different WGA methods in FFPE cancer specimens using targeted next-generation sequencing (NGS). We therefore tested the two most commonly used WGA methods, multiple displacement amplification (MDA-Qiagen REPLI-g kit) and the hybrid or modified PCR-based method (Sigma/Rubicon Genomics Inc. GenomePlex kit) in FFPE normal and tumor tissue specimens. For the normalized copy number analysis, the FFPE process caused none or very minimal bias. Variations in copy number were minimal in samples amplified using the GenomePlex kit, but they were statistically significantly higher in samples amplified using the REPLI-g kit. The pattern was similar for variant allele frequencies across the samples, which was minimal for the GenomePlex kit but highly variable for the REPLI-g kit. These findings suggest that each WGA method should be tested thoroughly before using it for clinical cancer samples.

An improved CTC isolation scheme for pairing with downstream genomics: Demonstrating clinical utility in metastatic prostate, lung and pancreatic cancer

Improvements in technologies to yield purer circulating tumor cells (CTCs) will enable a broader range of clinical applications. We have previously demonstrated the use of a commercially available cell-adhesion matrix (CAM) assay to capture invasive CTCs (iCTCs). To improve the purity of the isolated iCTCs, here we used fluorescence-activated cell sorting (FACS) in combination with the CAM assay (CAM + FACS). Our results showed an increase of median purity from the CAM assay to CAM + FACS for the spiked-in cell lines and patient samples analyzed from three different metastatic cancer types: castration resistant prostate cancer (mCRPC), non-small cell lung cancer (mNSCLC) and pancreatic ductal adenocarcinoma cancer (mPDAC). Copy number profiles for spiked-in mCRPC cell line and mCRPC patient iCTCs were similar to expected mCRPC profiles and a matched biopsy. A somatic epidermal growth factor receptor (EGFR) mutation specific to mNSCLC was observed in the iCTCs recovered from EGFR(+) mNSCLC cell lines and patient samples. Next-generation sequencing (NGS) of spiked-in pancreatic cancer cell line and mPDAC patient iCTCs showed mPDAC common mutations. CAM + FACS iCTC enrichment enables multiple downstream genomic characterizations across different tumor types.

Single-Nucleotide Polymorphism to Associate Cancer Risk

Genetic heterogeneity explains variation in predisposition for cancer. Whole-genome analysis allows risk to be quantified, giving better targeted screening and quantification of the personalized risk posed by environmental factors. Array-based approaches to whole-genome analysis are rapidly being overtaken by next-generation sequencing (NGS). In this review the different platforms currently available for NGS are compared and the opportunities and risks of this approach are discussed: including the informatics packages required and the ethical issues. Methods applicable to the personal genome machine (PGM) are given as an example of workflows.

Comparison of whole genome amplification methods for analysis of DNA extracted from microdissected early breast lesions in formalin-fixed paraffin-embedded tissue

To understand cancer progression, it is desirable to study the earliest stages of its development, which are often microscopic lesions. Array comparative genomic hybridization (aCGH) is a valuable high-throughput molecular approach for discovering DNA copy number changes; however, it requires a relatively large amount of DNA, which is difficult to obtain from microdissected lesions. Whole genome amplification (WGA) methods were developed to increase DNA quantity; however their reproducibility, fidelity, and suitability for formalin-fixed paraffin-embedded (FFPE) samples are questioned. Using aCGH analysis, we compared two widely used approaches for WGA: single cell comparative genomic hybridization protocol (SCOMP) and degenerate oligonucleotide primed PCR (DOP-PCR). Cancer cell line and microdissected FFPE breast cancer DNA samples were amplified by the two WGA methods and subjected to aCGH. The genomic profiles of amplified DNA were compared with those of non-amplified controls by four analytic methods and validated by quantitative PCR (Q-PCR). We found that SCOMP-amplified samples had close similarity to non-amplified controls with concordance rates close to those of reference tests, while DOP-amplified samples had a statistically significant amount of changes. SCOMP is able to amplify small amounts of DNA extracted from FFPE samples and provides quality of aCGH data similar to non-amplified samples.

Blood and tissue biomarkers in prostate cancer: state of the art

The prevalence of prostate cancer (PCa) is high and increases with age. PCa is the most common cutaneous cancer in American men. Prostate-specific antigen (PSA) screening has impacted the detection of PCa and is directly responsible for a dramatic decrease in stage at diagnosis. Gleason score and stage at the time of diagnosis remain the mainstay to predict prognosis, in the absence of more accurate and reliable tissue or blood biomarkers. Despite extensive research efforts, very few biomarkers of PCa have been introduced to date in clinical practice. Even screening with PSA has recently been questioned. A thorough analysis of all tissue and serum biomarkers in prostate cancer research cannot be easily synthesized, and goes beyond the scope of the present article. Therefore the authors focus here on the most recently reported tissue and circulating biomarkers for PCa whose application in clinical practice is either current or expected in the near future.

Bacterial artificial chromosome array-based comparative genomic hybridization using paired formalin-fixed, paraffin-embedded and fresh frozen tissue specimens in multiple myeloma

BACKGROUND

Multiple myeloma (MM) is a neoplasm of malignant plasma cells that often harbors many chromosomal aberrations. Currently, fresh frozen tissues (FT) are considered the most reliable for molecular genetic analysis; however, formalin-fixed, paraffin-embedded (FFPE) tissues are easily retrievable. Compared with conventional cytogenetics, bacterial artificial chromosome (BAC) array-comparative genomic hybridization (CGH) allows more sensitive detection of chromosomal abnormalities.

METHODS

The authors analyzed 7 paired FT and FFPE samples of bone marrow aspirate materials obtained from patients with MM in parallel to determine the efficacy of BAC array-CGH using FFPE.

RESULTS

Thirty-four aberrations were identified, including 29 that were observed in both sample types, yielding 85% concordance. Nonrandom anomalies, including gains on 7q, 9q, 15q, and 19p and losses on 8p and 13q, were observed in paired samples from at least 2 patients. To verify these results, fluorescence in situ hybridization (FISH) was performed using probes specific for 7q and 15q, and gains were observed in the 4 samples that were examined. Furthermore, 1 of 3 samples from patients who had monoclonal gammopathy of undetermined significance that were tested also carried gain on 7q, suggesting that this aberration may be an early transforming event.

CONCLUSIONS

The current results indicated that BAC array-CGH can be effective using FFPE samples and is a sensitive method for the identification of nonrandom chromosomal aberrations in MM.

A whole-genome amplification protocol for a wide variety of DNAs, including those from formalin-fixed and paraffin-embedded tissue

High-resolution genomic arrays and next-generation sequencers are some of the genome-based technologies poised to make significant contributions in the near future to basic and clinical science. The success of these technologies, and most certainly their translation into the clinic, will require that they produce high quality, reproducible data from small archived tumor specimens, including biopsies. DNA from patient samples, especially archival tissue, can be a limiting factor and lead to the need for amplification of the starting material. A variety of whole-genome amplification techniques are available, but choosing the most reliable, reproducible amplification technology that will be suitable for use across a wide spectrum of clinical specimens is essential. Sigma's whole-genome amplification kit provides a robust, highly reliable, and versatile amplification system across a variety of DNA sources. This chapter will detail Sigma's amplification protocol along with an optimized DNA extraction protocol for formalin-fixed and paraffin-embedded tissue.